FFmpeg 开发说明（七）：ffmpeg 解码保存为 PCM 的音频并使用软件播放
最编程
2024-05-02 22:10:08
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void FFmpegManager::testDecodeAudioForPcm()
{
// QString fileName = "test/1.avi";
QString fileName = "E:/testFile/3.mp4";
// QString fileName = "E:/testFile2/1.mp3";
QString outFileName = "D:/1.pcm";
AVFormatContext *pAVFormatContext = 0; // ffmpeg的全局上下文，所有ffmpeg操作都需要
AVCodecContext *pAVCodecContext = 0; // ffmpeg编码上下文
AVCodec *pAVCodec = 0; // ffmpeg编码器
AVPacket *pAVPacket = 0; // ffmpag单帧数据包
AVFrame *pAVFrame = 0; // ffmpeg单帧缓存
SwrContext *pSwrContext = 0; // ffmpeg音频转码
QFile file(outFileName); // Qt文件操作
int ret = 0; // 函数执行结果
int audioIndex = -1; // 音频流所在的序号
int numBytes = 0;
uint8_t * outData[2] = {0};
int dstNbSamples = 0; // 解码目标的采样率
int outChannel = 0; // 重采样后输出的通道
AVSampleFormat outFormat = AV_SAMPLE_FMT_NONE; // 重采样后输出的格式
int outSampleRate = 0; // 重采样后输出的采样率
pAVFormatContext = avformat_alloc_context(); // 分配
pAVPacket = av_packet_alloc(); // 分配
pAVFrame = av_frame_alloc(); // 分配
if(!pAVFormatContext || !pAVPacket || !pAVFrame)
{
LOG << "Failed to alloc";
goto END;
}
// 步骤一：注册所有容器和编解码器（也可以只注册一类，如注册容器、注册编码器等）
av_register_all();
// 步骤二：打开文件(ffmpeg成功则返回0)
LOG << "文件:" << fileName << "，是否存在：" << QFile::exists(fileName);
// ret = avformat_open_input(&pAVFormatContext, fileName.toUtf8().data(), pAVInputFormat, 0);
ret = avformat_open_input(&pAVFormatContext, fileName.toUtf8().data(), 0, 0);
if(ret)
{
LOG << "Failed";
goto END;
}
// 步骤三：探测流媒体信息
ret = avformat_find_stream_info(pAVFormatContext, 0);
if(ret < 0)
{
LOG << "Failed to avformat_find_stream_info(pAVCodecContext, 0)";
goto END;
}
LOG << "视频文件包含流信息的数量:" << pAVFormatContext->nb_streams;
// 步骤四：提取流信息,提取视频信息
for(int index = 0; index < pAVFormatContext->nb_streams; index++)
{
pAVCodecContext = pAVFormatContext->streams[index]->codec;
switch (pAVCodecContext->codec_type)
{
case AVMEDIA_TYPE_UNKNOWN:
LOG << "流序号:" << index << "类型为:" << "AVMEDIA_TYPE_UNKNOWN";
break;
case AVMEDIA_TYPE_VIDEO:
LOG << "流序号:" << index << "类型为:" << "AVMEDIA_TYPE_VIDEO";
break;
case AVMEDIA_TYPE_AUDIO:
LOG << "流序号:" << index << "类型为:" << "AVMEDIA_TYPE_AUDIO";
audioIndex = index;
break;
case AVMEDIA_TYPE_DATA:
LOG << "流序号:" << index << "类型为:" << "AVMEDIA_TYPE_DATA";
break;
case AVMEDIA_TYPE_SUBTITLE:
LOG << "流序号:" << index << "类型为:" << "AVMEDIA_TYPE_SUBTITLE";
break;
case AVMEDIA_TYPE_ATTACHMENT:
LOG << "流序号:" << index << "类型为:" << "AVMEDIA_TYPE_ATTACHMENT";
break;
case AVMEDIA_TYPE_NB:
LOG << "流序号:" << index << "类型为:" << "AVMEDIA_TYPE_NB";
break;
default:
break;
}
// 已经找打视频品流
if(audioIndex != -1)
{
break;
}
}
if(audioIndex == -1 || !pAVCodecContext)
{
LOG << "Failed to find video stream";
goto END;
}
// 步骤五：对找到的音频流寻解码器
pAVCodec = avcodec_find_decoder(pAVCodecContext->codec_id);
if(!pAVCodec)
{
LOG << "Fialed to avcodec_find_decoder(pAVCodecContext->codec_id):"
<< pAVCodecContext->codec_id;
goto END;
}
#if 0
pAVCodecContext = avcodec_alloc_context3(pAVCodec);
// 填充CodecContext信息
if (avcodec_parameters_to_context(pAVCodecContext,
pAVFormatContext->streams[audioIndex]->codecpar) < 0)
{
printf("Failed to copy codec parameters to decoder context!\n");
goto END;
}
#endif
// 步骤六：打开解码器
ret = avcodec_open2(pAVCodecContext, pAVCodec, NULL);
if(ret)
{
LOG << "Failed to avcodec_open2(pAVCodecContext, pAVCodec, pAVDictionary)";
goto END;
}
// 打印
LOG << "解码器名称：" <<pAVCodec->name << endl
<< "通道数：" << pAVCodecContext->channels << endl
<< "通道布局：" << av_get_default_channel_layout(pAVCodecContext->channels) << endl
<< "采样率：" << pAVCodecContext->sample_rate << endl
<< "采样格式：" << pAVCodecContext->sample_fmt;
#if 1
outChannel = 2;
outSampleRate = 44100;
outFormat = AV_SAMPLE_FMT_S16P;
#endif
#if 0
outChannel = 2;
outSampleRate = 48000;
outFormat = AV_SAMPLE_FMT_FLTP;
#endif
LOG << "to" << endl
<< "通道数：" << outChannel << endl
<< "通道布局：" << av_get_default_channel_layout(outChannel) << endl
<< "采样率：" << outSampleRate << endl
<< "采样格式：" << outFormat;
// 步骤七：获取音频转码器并设置采样参数初始化
// 入坑二：通道布局与通道数据的枚举值是不同的，需要转换
pSwrContext = swr_alloc_set_opts(0, // 输入为空，则会分配
av_get_default_channel_layout(outChannel),
outFormat, // 输出的采样频率
outSampleRate, // 输出的格式
av_get_default_channel_layout(pAVCodecContext->channels),
pAVCodecContext->sample_fmt, // 输入的格式
pAVCodecContext->sample_rate, // 输入的采样率
0,
0);
ret = swr_init(pSwrContext);
if(ret < 0)
{
LOG << "Failed to swr_init(pSwrContext);";
goto END;
}
file.open(QIODevice::WriteOnly | QIODevice::Truncate);
outData[0] = (uint8_t *)av_malloc(1152 * 8);
outData[1] = (uint8_t *)av_malloc(1152 * 8);
// 步骤七：读取一帧数据的数据包
while(av_read_frame(pAVFormatContext, pAVPacket) >= 0)
{
if(pAVPacket->stream_index == audioIndex)
{
// 步骤八：将封装包发往解码器
ret = avcodec_send_packet(pAVCodecContext, pAVPacket);
if(ret)
{
LOG << "Failed to avcodec_send_packet(pAVCodecContext, pAVPacket) ,ret =" << ret;
break;
}
// 步骤九：从解码器循环拿取数据帧
while(!avcodec_receive_frame(pAVCodecContext, pAVFrame))
{
// nb_samples并不是每个包都相同，遇见过第一个包为47，第二个包开始为1152的
// LOG << pAVFrame->nb_samples;
// 步骤十：获取每个采样点的字节大小
numBytes = av_get_bytes_per_sample(outFormat);
// 步骤十一：修改采样率参数后，需要重新获取采样点的样本个数
dstNbSamples = av_rescale_rnd(pAVFrame->nb_samples,
outSampleRate,
pAVCodecContext->sample_rate,
AV_ROUND_ZERO);
// 步骤十二：重采样
swr_convert(pSwrContext,
outData,
dstNbSamples,
(const uint8_t **)pAVFrame->data,
pAVFrame->nb_samples);
// 第一次显示
static bool show = true;
if(show)
{
LOG << numBytes << pAVFrame->nb_samples << "to" << dstNbSamples;
show = false;
}
// 步骤十四：使用LRLRLRLRLRL（采样点为单位，采样点有几个字节，交替存储到文件，可使用pcm播放器播放）
for (int index = 0; index < dstNbSamples; index++)
{
for (int channel = 0; channel < pAVCodecContext->channels; channel++) // 交错的方式写入, 大部分float的格式输出
{
// 用于原始文件jinxin跟对比
// file.write((char *)pAVFrame->data[channel] + numBytes * index, numBytes);
file.write((char *)outData[channel] + numBytes * index, numBytes);
}
}
av_free_packet(pAVPacket);
}
}
}
file.close();
END:
LOG << "释放回收资源";
if(outData[0] && outData[1])
{
av_free(outData[0]);
av_free(outData[1]);
outData[0] = 0;
outData[1] = 0;
LOG << "av_free(outData[0])";
LOG << "av_free(outData[1])";
}
if(pSwrContext)
{
swr_free(&pSwrContext);
pSwrContext = 0;
}
if(pAVFrame)
{
av_frame_free(&pAVFrame);
pAVFrame = 0;
LOG << "av_frame_free(pAVFrame)";
}
if(pAVPacket)
{
av_free_packet(pAVPacket);
pAVPacket = 0;
LOG << "av_free_packet(pAVPacket)";
}
if(pAVCodecContext)
{
avcodec_close(pAVCodecContext);
pAVCodecContext = 0;
LOG << "avcodec_close(pAVCodecContext);";
}
if(pAVFormatContext)
{
avformat_close_input(&pAVFormatContext);
avformat_free_context(pAVFormatContext);
pAVFormatContext = 0;
LOG << "avformat_free_context(pAVFormatContext)";
}
}